Brining - the science

By JOE O'CONNELL, cbbqa Past President
Last updated November 27, 2001

Note: This article is based on the
research and writings of Kit Anderson and Bill Wight,
both of whom are nationally recognized barbecue science experts, as
well as Harold McGee, author of On Food and Cooking.
These three authorities deserve all the credit for the following
analysis, but this author takes full responsibility for all errors and
omissions.

Meat will dry out when covered with
salt, but brining seems to make meat moister. Since a brining
solution is
simply water and salt (with perhaps some spices added for flavor), is there a contradiction here?
Should brining not result in dried-out meat rather than moister
meat? The following explains the "why" for the curious.

Cooks who are not so
curious may skip the science but remember two simple rules:

Putting dry salt on raw meat will dry it out; but

Brining meat (especially poultry) will make it moist.

Because salt dries out the surface of meat, the general rule is to salt
meat after cooking, unless there is a specific reason that the meat's
surface should be dried out before cooking. For example, many barbecue rubs
contain salt for the purpose of drying the meat's surface to make it
crusty.

Also, most poultry
(chicken and turkey) should be brined before it is put in the pit for
barbecue, because the low 'n slow barbecue method tends to dry out
poultry, and brining helps keep it moist.
Now, for the science.

Meat structure

Meat is muscle tissue, which in turn is made up of individual cells
and connective tissue. Meat is composed primarily of two types of
cells:

muscle cells

fat cells

These cells and connective tissue are in turn made up primarily of
four types of molecules, and their percentage presence in lean meat are
(see McGee at 87):

water (75%)

protein (18%)

fat (3%)

carbohydrates (trace)

Muscle cells

The muscle cells of meat are long, thin fibers, some of which exceed
twelve inches in length. The individual fiber cells are bound
together by thin sheets of connective tissue, which is not itself living
tissue but a protein structure which surrounds the live cells that
created them. Bound fiber cells are grouped together in bundles to
form individual muscles. McGee at 87-89.

Fat cells

Meat also includes fat tissue. Some fat is dispersed invisibly
among other tissues, but most fat in meat is concentrated in adipose
tissue, which is composed of specialized fat cells. McGee at
530.

Adipose tissue is the fat tissue which surrounds muscle tissue.
Marbling refers to the fat tissue which is incorporated into the
muscle tissue and appears as patterns of white splotches in the red
matrix of muscle. McGee at 90.

Fat cells contain a high percentage of water than other meat cells,
and it is the water content of fat which makes cooked meat
moist.

Carbohydrates

Carbohydrates are sugars and long chains of sugar molecules, like
starch. In meat, most carbohydrates are converted into glucose,
which is the preferred food of muscle cells. While most cells can
burn fats for energy, the brain and other nerve cells can use only
glucose.

Glucose is stored in meat tissue as glycogen. Glycogen is
stored in the liver and throughout muscle tissue. McGee at 527 ff.

Proteins

Proteins are molecular structures composed of carbon, hydrogen,
oxygen and nitrogen. There are many different types of proteins,
but all proteins are built from a few basic units, called amino
acids. Proteins include many different types:

enzymes that build up and break down other molecules

antibodies that fight disease

hemoglobin, which carries oxygen to cells

insulin and other hormones

muscle and other tissue

Proteins are the largest component after water in meat (muscle),
internal organs, bones, blood cells, skin, hair, and teeth.

Fats

Fats are specialized molecules which are used by muscle and other
cells as one of the two primary sources of energy (the other source is
carbohydrates). Measured by weight, fats store twice as much
energy as carbohydrates.

Fats in cooked meat give the meat more flavor, a smoother texture and
account for the sensation of "fullness" when eaten.
McGee at 530.

Fat molecules are present in meat cells -- in the cell membranes and
cytoplasm. Fat molecules are the primary component of fat cells,
which are storage tanks for fat molecules held in a network of
connective tissue -- fat tissue or adipose tissue -- which helps insulate the muscles and
provide a source of reserve energy. McGee at 90.

Water

Water molecules are found both inside the cells (intracellular water)
and in the space surrounding the cells (intercellular water). Some
water molecules are free -- either unbonded or very lightly bonded with
other molecules -- while some water molecules are bonded tightly with
proteins and other molecules.

Meat cells are contained by cell membranes that keep the cell contents
from flowing into the intercellular spaces, and the cell membranes keep most
molecules from penetrating into or exiting out of the cells. Most
molecules cannot penetrate through the cell membrane from outside a cell,
but there are exceptions, as will be described below in the discussion
of osmosis.

There are several different kinds of cells in meat tissue, and each
kind contains different amounts of water. The cells that contain
the most intracellular water are the fat cells. The reason that a
Prime Grade beef steak is moister than the same cut of Select Grade
steak is that the Prime Grade meat contains many more fat cells, which
contain many more water molecules, which means that the steak will be
moister when cooked and eaten.

Proteins chains

Inside each kind of meat cell, there are many different bundles of long proteins.
Proteins are complex chains of molecules which can hold other molecules,
like water. Normally, proteins are coiled up tightly with bonds that hold them in single units.
Tightly coiled proteins cannot bind with very many water molecules.

However, when a protein is cooked (by heat, acid or drying -- this is
very important, since drying, as by sodium, "cooks" protein),
the protein bonds break down, and the protein bundles straighten out. This is called
denaturing. When proteins are denatured, they can bond
together with other molecules, like water and other denatured
proteins. This
is
called coagulation.

This process is seen as a raw egg begins to cook:

When the raw egg is first put into the frying pan, the egg white is
clear,
because there is a lot of room for light to go between the molecules.

As
the egg begins to cook, the protein bonds break down -- denature
-- and then the proteins begin to bond with other molecules, including
other denatured proteins and free (unbonded) molecules of water -- coagulation.
As the coagulation progresses, there is no longer enough room for light to
penetrate, so the egg white becomes opaque (light cannot go through),
and the color of the egg changes from clear to white.

At this point, just after the egg has changed color, there is a lot of moisture
(water molecules) trapped by these barely cooked proteins. This is when
the egg white is juiciest
and
most tender.

This same process applies not just to eggs but to all meat.

Water within meat

As the internal temperature of meat proteins remains between 100°F
and 120°F, the protein bundles shrink slowly in size, but the proteins
continue to bond with water molecules, so there is minimal moisture
loss.

However, as the temperature of the proteins reaches and passes
120°F, significant moisture loss begins to occur, because the proteins
cannot retain the bonds with the water molecules. The water
molecules flow from the meat and are lost. This is popularly
called the first sweat. The first sweat results as water
molecules are unbonded and freed from the space
between the individual cells. Note that the first sweat is not
evaporation but the freeing of water molecules from the intercellular
spaces and protein bonds.

The second sweat takes place when the cells
themselves begin to break down, which occurs normally when the internal
temperature of the meat cells exceeds 140°F. At this temperature,
the individual cells break apart and release the cells' contents,
including the unbonded proteins and molecular (free) water. This
loss of intracellular molecular water at a temperature above 140°F gave
rise to the term second sweat.

Salt and osmosis

As described above, 120°F and 140°F are the normal temperatures at
which intercellular water molecules and intracellular water molecules,
respectively, are released from meat proteins and may be lost during
cooking. However, these temperatures can be increased by brining
or salting, through the process of osmosis.

As described above, the cell membrane of all animal cells keeps the
intracellular proteins and other molecules inside the cell and keeps the
intercellular molecules outside the cell. But there is an
exception: water can pass through a cell membrane in certain
circumstances.

Salt

There are many different kinds of salts, which are the reaction
product of an acid on a metal. Here the word salt will be
used to refer to ordinary table salt.

Salt (ordinary table salt, to be precise) is a molecule of sodium
chloride. That is, table salt is a molecule that combines one atom of
sodium (Na) and one atom of chlorine (Cl), which forms a molecule of
sodium chloride (NaCl), which combines in a cubic crystalline form when
dried.

Inside muscles (meat), sodium and chlorine are separate atoms:
sodium is a positively charged ion, and chlorine is a negatively charged
ion. With other elements like potassium and phosphorus, they
regulate the concentrations of other chemicals inside and outside
cells.

Sodium and chloride are the principal mineral atoms in the blood
plasma, and potassium and phosphate are the principal mineral atoms in
the cellular cytoplasm. McGee at 544.

Osmosis

Sodium and other mineral atoms act across the semipermeable cell membranes
form an area of higher concentration to an area of lower
concentration, in a process called osmosis. Osmosis means the
diffusion of certain molecules across the semipermeable cell membranes
(walls) in order to equalize the ion concentrations of either
side. McGee at 544.

In living tissue, osmosis is important to maintain life itself.
For example, if there is "too much" sodium in the blood --
i.e., if there is a higher concentration of sodium in the blood than in
the muscle cells -- then water molecules will pass through the cell membranes
and into the blood. This will increase the number of water
molecules in the blood and thus reduce the sodium concentration in the
blood, while at the same time it will decrease the number of water
molecules inside the cells and thus increase the potassium concentration
inside the cells.

Again -- this is critically important to an understanding of brining
-- if the percentage concentration of sodium on the outside of a cell is
higher than the concentration of sodium on the inside of a cell, then
free water molecules will pass from inside the cell, through the cell membrane, and into the intracellular space. McGee at 544.

The process of osmosis is a requirement for the survival of living
cells, because it regulates the concentration of minerals. But
osmosis is a chemical property and does not require living tissue in
order to operate. Thus, osmosis -- the diffusion of water across a
cell membrane -- works in non-living tissue and is the basis for brining.

Brining

Brine is a concentration of water and salt, typically in the ratio of
16 parts of water to 1 part of salt (such as 2 gallons of water with 2
cups of Kosher salt).

Brining operates on the principal of osmosis, as explained
above. The brining liquid has a higher concentration of sodium
than the meat's intercellular spaces. In a series of reactions,
both the number of sodium molecules and the number of free water
molecules increase in meat's intercellular spaces, and the sodium
concentration increases in the meat's intracellular fluids.

As the meat remains in the brining solution for many hours, the
process of osmosis causes the free water molecules in the intracellular
fluids to exit the cells. Contrary to popular belief, sodium does
not pass from the brining solution across the cell membrane into the cell,
but there is some increase in the sodium in the intercellular spaces by
the simple process of diffusion.

Therefore, during brining, the free (unbonded) water molecules inside the cells move
through the cell membranes and exit out to the intercellular spaces.
This appears to accomplish exactly the opposite effect that is intended
by brining, because this would seem to make the meat drier. But
the process continues . . .

As the free water molecules leave the meat cells, there is an
increase in the sodium concentration inside the cells. The
concentration increases because of the loss of water, not because of a
gain of sodium. As the concentration of sodium increases, the
sodium "cooks" the intracellular proteins, denaturing
them. The denatured proteins then cross link and bond with the
free water molecules -- remember how the raw egg turned white -- forming
a tight molecular bond between the protein chain and the water
molecule. Now, the water is trapped in the protein and is no
longer a free water molecule, so these water molecules will not exit the
cell. This cross linking of protein and water molecules means the cells
will not break
up
and
lose their moisture at the normal temperature of unbrined meat -- higher temperature than unbrined meat.

In summary, the brining causes an increase in the cellular sodium
concentration, which denatures the proteins, which cross-link to form
tight bonds with the previously free water molecules, which resist
breaking apart except at a higher-than-normal
temperature.

Brining thus increases the temperature at which the protein and water
bonds will break and release their bound water molecules. In other
words, brining causes some free water molecules to exit the cells while
the remaining water molecules are trapped and bonded tightly to the
denatured protein chains, which remain stronger with the presence of the
increased sodium concentration. As a result, the temperature of
the so-called second sweat will increase from 140°F to perhaps
160°F. As a further result of this increase in temperature, the
meat will cook but still retain the moisture that would normally have
been lost.

Misconceptions

There are several popular misconceptions about brining:

Brining causes an increase in the sodium inside the cells;

Brining adds water to the meat, which will make it
moister; and

Brining makes meat more tender.

These are misconceptions, but they are only wrong by a little.

Sodium in meat cells

As explained above, the brining solution by the process of osmosis
causes intracellular free water molecules to exit the cells.
However, brining does not cause sodium to enter the cells. It only
seems so.

There is no diffusion of sodium into the meat cells,
because the cells themselves already contain a high concentrations of sodium. Even very concentrated
brining solutions will be less concentrated
than
the intracellular fluids.

However, as the intracellular fluids lose their free water molecules,
their concentration of sodium increases, because of the loss of
water. Therefore, the cells seem to have increased their sodium
content, but this is only an illusion.

In the case of the intercellular spaces, however, brining does cause
an increase in sodium concentration, not by the process of osmosis
(there are no cell membranes) but by the process of diffusion.

Moister meat

It is true that brined meat will be moister than unbrined meat, but
not because of the added water.

Yes, it is true that brining meat increases the water content of the
meat. In fact, a brined turkey will gain about 20% in weight.
For example, a 15 lb. turkey will weigh about 18 lbs after brining
overnight. However, virtually all this extra water is contained in
the intercellular spaces and will be lost when the internal temperature
reaches 120°F, during the so-called first
sweat. By the time the meat is cooked, all of this added water
(and much of the natural water) will have left the meat.
Therefore, the water added by brining will not remain during cooking to
make the meat moister.

The brined meat is moister because of the added salt in the
intercellular fluids. As explained above, heat makes proteins
denature and coagulate. Without brining, the cells disintegrate
and release their intercellular fluids at a temperature of 140°F -- the
so-called second sweat. However, with brining, the increased
sodium within the cells causes the cells to remain intact until the
internal temperature reaches 160°F. This means that the cellular
fluids are retained in the meat, so the meat is moister.

Tender meat

Brining does not cause the meat to be more tender, at least not
directly, in the way that a marinade
does. Brining makes three changes which seem to make the meat more
tender:

Moister

Better texture

More flavor

Brining increases the temperature at which the meat cells like collagen
will break down, and this in turn keeps the meat from losing the
intercellular water molecules and drying out. Thus, the meat is
moister.

In addition, the increased water retention lubricates the
individual muscle fibers, which improves the texture of the cooked
meat. Finally, the increased sodium improves or brings out the flavor
of the meat.

The combination of meat that is moister, has a better texture and is
more flavorful seems to make the meat more tender, but this is not
really so.

Brining red meat

Brining does not produce a desirable result in all meat, especially
red meat.

With brining, the flavor change in red meat produces a ham-like
flavor. While desirable in smoked pork chops, ham, bacon, corned
beef,
prosciutto, and pastrami, this change in the meat's flavor is not appropriate for traditional forms
of barbecue meat, such as pork ribs, pork shoulder and beef brisket.